There is an old adage, “generals always prepare to fight the last war.” It is an old adage because it is a true one. Northern artillerymen set up their cannon for the first battle of the Civil War, confident that they could obliterate the Southern infantry long before coming under fire themselves. Cavalry featured prominently in the European armies of 1914, until machine guns mowed down men and horses alike. France used the lessons of trench warfare to build the Maginot Line by 1940, only to see German tanks easily outflank it.

Things are no different today. President Donald Trump has just asked Congress for a $6 billion supplemental defense budget, much of it to be used to “blow North Korean missiles out of the sky” if the Koreans should be so bold, or foolish, to threaten American allies such as Japan. American B-1 and B-2 bombers have prowled the skies of Northeast Asia to remind Pyongyang of the damage the United States could do even with conventional weapons. And if North Korea should be so rash as to employ its own modest nuclear arsenal, it would be turned into a radioactive wasteland by even a limited American retaliation.

Or so goes the argument of those generals and armchair generals always preparing to fight “the last war.”  To them, this “last war” was the Cold War, and planning for fighting a “hot” version of it invariably centered around the possibility of a full exchange of nuclear weapons between the United States and Soviet Union.

Of course, that “last war” was never fought at all. The Cold War between the United States and Soviet Union never turned hot because both sides realized the horrors that would result, even on such occasions as the 1962 Cuban Missile Crisis, during which the United States held a considerable edge in numbers of atomic weapons and means to deliver those weapons. Still, the dominant model of a major war — a nuclear war — persists in the minds of nearly everyone now imagining the likely trajectory of the current escalating crisis between the United States and North Korea.

Such a war, if it is ever fought, will not be nuclear. And it will not be won by the United States.

There is something far faster, and ultimately far more lethal, than a nuclear-tipped missile. It is a bit of computer code designed to wreak instantaneous havoc with its target. It is cyber-warfare.

One highly likely target in any cyber-war is the enemy’s energy grid. Why destroy a city — a country, even — when you can simply darken it for a year or more and let its inhabitants take care of the rest as they desperately seek food, fuel and the other necessaries of life? The energy grid of the United States is about as well protected from software corruptions that would physically shatter hardware, such as the highly sophisticated turbines and other key components generating electricity, from drone strikes. There are no federal regulations stipulating high levels of cyber defenses, and none likely to be instituted anytime soon by a government uninterested in “shackling” private businesses with such regulations. A cyber strike could easily instantly destroy a substantial portion of America’s capacity to generate electricity. And those turbines cannot be easily or instantly replaced. They can take years to build, assuming the materials and energy to build them can be found.

One might argue that the same Cold War principle of “Mutually Assured Destruction” ought to prevent a cyberwar exchange, too. If North Korea cripples our power grid, we could cripple theirs. To this argument, I would point to a famous photograph taken from space, showing South Korean, Japanese, and Chinese cities brilliantly illuminated at night. North Korea, by contrast, is a sea of darkness. At the time the photograph was taken, it was interpreted as a sign of a severe energy shortage in North Korea, which indeed suffered from such a shortage.

But it is possible to see that photograph a bit differently. Which country, North Korea or the United States, has a society better equipped to survive a year or two without electricity? Which country, to put it another way, is more likely to lose a cyber-war with the other? To me, the answer is clear, and it is one that does not inspire much confidence in the reckless leadership currently in Washington. President Trump wants billions to shoot down North Korean missiles? He might as well be asking for more horses and sabers.

Michael A. Barnhart is a professor of history with a focus on United States foreign relations at Stony Brook University.

Correction: Nov. 13, 2017

In a previous version of this story, Andrew Goldstein was incorrectly listed as the author for this letter to the editor. The letter was written by Michael A. Barnhart.